1. Field
One embodiment of the invention relates to a magnetic storage medium, an information storage device, and a control device.
2. Description of the Related Art
In recent years, information storage devices such as a hard disk drive (HDD) have been desired to have a high recording density, due to a high transmission rate or an increase in capacity of a magnetic storage medium used in the information storage devices.
Accordingly, various recording methods, such as a discrete track recording method or a patterned media recording method (also referred to as bit patterned media (BPM)) for realizing high recording density in the magnetic storage medium have been suggested. The discrete track recording method forms non-magnetic areas between adjacent tracks and records data only in track portions formed by magnetic bodies. The patterned media recording method isolates each of the magnetic particles to produce a single bit pattern, thereby improve a record resolution.
The patterned media have high recording density. The patterned media corresponds to a magnetic recording medium on which magnetic areas are separated and isolated from each other by non-magnetic areas. Here, the magnetic areas are areas where data is written to and read out from. A plurality of magnetic dots can be disposed in the patterned media. The recording density of the patterned media can be improved by increasing the number of the magnetic dots.
In a common information storage device, a positioning signal is readout from a servo pattern on the medium, and a magnetic head is positioned according to the positioning signal. Further, tracks of magnetic recording medium are formed by forming process such as electron beam lithography and nano-imprint. However, a track oscillation is caused during the forming process. As a result, the magnetic head cannot be accurately positioned using only the information of the servo pattern.
Therefore, conventionally, in order to improve the positioning precision, a reference signal is written in a data recording track, the track oscillation is detected from an amplitude variation of the reproduced reference signal, and feedforward control is performed based on the detected result. However, the process of investigating the track oscillation needs to be executed in advance. That is to say, for example, confirmation becomes necessary whenever disturbance such as a temperature change occurs. Therefore, device performance may be deteriorated.
In order to prevent the deterioration of the device performance, the number of servo areas per track may be increased to increase the amount of servo information to be sampled. Accordingly, a servo control band is increased. However, the increase in the servo areas decreases the data areas, thereby lowers a recording density per unit area.
As the aforementioned kind of positioning control method, a record reading method such as the one disclosed in Japanese Patent Application Publication (KOKAI) No. 2003-157631 has been suggested. This record reading method stores various signal patterns acquired from magnetic dot arrangement. Then, the record reading method compares the signal patterns with track shift signals of when the head position is offset from a central track, and estimates a positioning error amount based on the matched signal pattern and track shift signal.
When writing data by a magnetic head, magnetic dots to be recorded need to be located directly under the magnetic head. That is, it is important to generate a clock signal synchronized with an arrangement pattern of a magnetic body, while predicting positions of the magnetic dots on the magnetic recording medium.
Conventionally, as disclosed in Japanese Patent Application Publication (KOKAI) No. 2003-157631, a shift direction of the magnetic head can be acquired. However, the actual shift amount of the magnetic head cannot be continuously acquired, so that the accuracy in controlling the magnetic head to be positioned at the center of the track is lowered.